From the Guidelines
A reduction in urea from 41 to 14 mmol/L over 48 hours during CRRT is generally considered safe, but it is crucial to monitor for symptoms of disequilibrium syndrome, particularly in patients with impaired renal function. When starting CRRT, the recommended safe rate of urea reduction is approximately 25-30% in the first 24 hours to avoid dialysis disequilibrium syndrome (DDS) 1. Your patient's reduction represents about a 66% decrease over 48 hours, which averages to roughly 33% per day - slightly higher than the conservative recommendation but still within a reasonable range for most patients.
Key Considerations
- The risk of disequilibrium syndrome is highest when urea is lowered too rapidly, particularly in patients with very high initial levels (>35 mmol/L) or those with risk factors like neurological conditions, liver disease, or pediatric patients.
- Disequilibrium syndrome occurs because rapid removal of urea from the blood creates an osmotic gradient between the blood and brain, causing cerebral edema.
- Symptoms to monitor for would include headache, nausea, vomiting, altered mental status, seizures, or coma.
Recommendations for CRRT Initiation
- For future CRRT initiations in patients with severe uremia, using a lower blood flow rate, reduced dialysate flow, or intermittent CRRT for the first 24-48 hours can help achieve a more gradual urea reduction.
- Individualization of the intensity of CRRT may be required to meet a patient’s requirements for maintenance of electrolyte and fluid balance, as suggested by the Canadian Society of Nephrology commentary on the 2012 KDIGO clinical practice guideline for acute kidney injury 1.
- It is essential to consider the actual delivered dose of CRRT, which may be lower than the prescribed dose due to factors such as circuit clotting, medical imaging, and surgery, and to adjust the treatment accordingly.
From the Research
Safe Rate of Urea Reduction
- The safe rate of urea reduction when initiating Continuous Renal Replacement Therapy (CRRT) is not explicitly stated in the provided studies, but a decrease from 41 mmol/L to 14 mmol/L in 48 hours may be considered relatively rapid 2, 3.
- A study on the lower limit of intensity to control uremia during CRRT suggests that a prescribed intensity of approximately 15 mL/kg/h might be adequate to control uremia for patients with severe acute kidney injury (AKI) 4.
Risk of Disequilibrium Syndrome
- Disequilibrium syndrome is a severe complication associated with dialysis treatment, and its risk factors include initial dialysis treatment, uraemia, metabolic acidosis, and extremes of age 2, 5.
- A decrease from 41 mmol/L to 14 mmol/L in 48 hours may be associated with a risk of disequilibrium syndrome, especially in patients with impaired renal function, as it represents a relatively rapid reduction in urea levels 2, 3.
- The pathophysiology of disequilibrium syndrome is not fully understood, but it is thought to be related to the shift of urea between brain intracellular space and plasma, and transient paradoxical metabolic acidosis within the central nervous system 5.
Prevention and Treatment
- Prevention of disequilibrium syndrome is crucial, and measures such as continuous renal replacement therapies may be effective in reducing the risk 5.
- Once established, treatment of disequilibrium syndrome should be focused on supportive therapy, and errors in fluid prescription, compounding, or delivery can be rapidly fatal 6.